At least 25% of the natural gas produced in the United States has an H.sub.2 S content of greater than 4 parts per million and is therefore classified as "sour." The H.sub.2 S is an environmental hazard, rendering the gas unacceptable for transport or use. The problem of H.sub.2 S gas arises from fossil fuels in general, such as petroleum, coal and lignite. The sulfur present in these materials is converted to H.sub.2 S by hydrogenation when these materials are converted to gaseous fuels such as refinery gas, coal gas and blue-water gas. Here as well, the sulfur value of the H.sub.2 S is lost unless the H.sub.2 S is converted to elemental sulfur, and use of the fuels without complete removal of the H.sub.2 S raises a risk of hazardous emissions. For these reasons, plus the value of sulfur itself, the treatment of these gases to remove the H.sub.2 S and convert it to elemental sulfur is of major importance to the chemical and energy industries.
The process commonly used at present for conversion of H.sub.2 S recovered from gases of this type to elemental sulfur is the Claus process. This process raises concerns relating to sulfur oxide emissions, however, since the process involves the formation of SO.sub.2 by oxidation of H.sub.2 S in air as an intermediate toward the production of elemental sulfur. Treatment of the tail gas from this process to eliminate the SO.sub.2 raises the cost of the process significantly. A further disadvantage of the process is the loss of the potential fuel value of the hydrogen content of the gas, since hydrogen is converted in the Claus process to water.
A process proposed by Bowman, U.S. Pat. No. 4,999,178, issued Mar. 12, 1991, claimed an alternative method of recovering sulfur from H.sub.2 S using the reaction between H.sub.2 S and CO.sub.2 instead of H.sub.2 S and SO.sub.2. Bowman taught that this reaction was: EQU CO.sub.2 +H.sub.2 S.revreaction.CO+H.sub.2 O+1/2 S.sub.2 ( 1)
The sulfur produced by this reaction is recovered by condensation, and the carbon monoxide is reacted with water vapor to produce hydrogen gas and carbon dioxide: EQU CO+H.sub.2 O.revreaction.CO.sub.2 +H.sub.2 ( 2)
This effects oxidation of the H.sub.2 S to elemental sulfur without requiring the use of air as an oxidant.